1. Field of the Invention
Our invention relates to fired equipment systems that discharge environmentally friendly exhaust gases and methods of operating such systems. In particular, our invention includes a stationary industrial burner in combination with a catalyst bed that converts pollutants generated by the burner to exhaust gases that require no further treatment before discharge to the atmosphere.
2. The Prior Art
Industrial burners are designed to generate heat and produce high combustion temperatures, typically in the range of from 2500 to 3000° F. At such temperatures, thermal nitrogen oxides (NOx) can form as gaseous byproducts of the combustion of air and the gas used as the fuel in the burners. These NOx byproducts, along with nitrogen oxides formed from the nitrogen containing compounds found in the fuel, are a major source of air pollution and governmental authorities have instituted strict environmental regulations limiting the amount of NOx gases that can be emitted into the atmosphere. Other pollutants generated by the combustion of fuel and air in the burner include carbon monoxide (CO) and volatile hydrocarbons (VOC's). Examples of such industrial burners are described in U.S. Pat. Nos. 5,073,105 and 6,007,325. To reduce or eliminate these nitrogen oxide pollutants the art has relied on selective catalytic reduction (SCR) of the flue gases exiting fired equipment. Unfortunately, SCR is designed to reduce primarily only the nitrogen oxide flue gas pollutants by injecting a reducing agent, such as, ammonia or urea, into the flue gas upstream of a catalyst bed to convert the NOx to nitrogen and water. Other pollutants may or may not be reduced from the flue gas. Urea is typically selected over ammonia in some applications because ammonia is poisonous and difficult to handle. Such systems are also complicated in that they require an assortment of different equipment and operating parameters to 1) inject the reducing agent(s) into the flue gas stream, 2) to mix the vaporized reducing agent and flue gas, 3) to allow sufficient residence time for the catalytic reaction, 4) to store the bulk reducing agent, and 5) to vaporize the reducing agent before injection. U.S. Pat. No. 3,887,683 describes such a SCR process to treat waste gases. Clearly a need exists for a simpler and more cost effective process to reduce pollutants generated by stationary fired equipment.
Our invention solves the problems currently associated with SCR processes by employing a process that does not require the injection of a reducing agent. Specifically, our invention utilizes a three-way catalyst composition, sometimes referred to as Non-selective Catalytic Reduction (NSCR). NSCR is best known for its use in treating exhaust in automobiles or other internal combustion engines and using catalyst compositions of the type described in U.S. Pat. No. 4,299,734. The use of our invention as described more fully below compared to traditional SCR processes results in lower capital cost for equipment, lower non-energy operating costs, lower energy costs, less physical area required for equipment and elimination of potential safety issues resulting from the use of ammonia. These and other benefits will become apparent from the following description, drawings and appended claims.